Atomic layer deposition (ALD) is a thin film deposition method that allows for the deposition of films having thicknesses on the order of nanometers in a precisely controlled way. Typically, ALD uses two or more gaseous precursors that are alternately and repeatedly applied to a substrate. A series of sequential steps in which a surface of the substrate is exposed to all precursors is called a deposition cycle. Each deposition cycle grows a single monolayer of film, or a fraction of a monolayer. This is due to the fact that, in ALD, film growth depends on chemisorption, a process whereby a precursor molecule adheres to a substrate's surface through the formation of a chemical bond (without further thermal decomposition of the precursor molecule taking place). Chemisorption stops naturally when all substrate surface sites available for chemical bonding with a precursor have been covered. Consequently, ALD is a self-limiting layer-by-layer deposition method that offers highly conformal coating and excellent thickness control. These characteristics make it a method of interest to various industries, among which in particular the semiconductor, and more specifically, the solar cell industry.
In the solar cell industry, ALD may be used to deposit aluminum oxide (Al2O3) films for the passivation of advanced mono-Si solar cells. To this end typical film thicknesses of 5-15 nm are required, which can be achieved using traditional single or multi-wafer ALD systems. Currently, the throughput of the most efficient multi-wafer ALD systems at said film thickness is about 60 wafers per hour. The amount of surface area to be treated in order to obtain—for example—a solar cell panel for use on a rooftop, is considerable however. And with the demand for solar cell panels on the rise, there is an increasing need for ALD apparatus featuring a higher throughput. Of course, the solar cell industry is exemplary only, and merely one of many industries in which the continual pressure for ALD equipment having an increased throughput is felt.
Such higher throughput is preferably achieved using apparatus that are relatively simple from a constructional point of view. This is because, typically, the simpler an apparatus is, the more economically it may be built, the more reliable it is and the less servicing it requires. It is therefore an object of the present invention to provide a device and a method for atomic layer deposition offering an improved throughput capacity at a minimum level of constructional complexity.